a. Field of the Invention
This invention relates to methods of annealing tows of acrylonitrile-containing filaments.
B. Prior Art
In the manufacture of acrylonitrile-containing filaments by certain processes, it is necessary to anneal or heat treat the filaments and simultaneously allow them to shrink in order to prevent subsequent filament fibrillation. The conventional method of annealing acrylonitrile-containing filaments is a batch process, where a tow of the filaments is placed in an autoclave and the autoclave filled with steam under pressure. Disadvantages of this method are that it is a batch process and that excessive handling of the filaments is required.
Attempts have been made to anneal acrylic filaments by continuous processes at steam pressures above atmospheric. In some of these attempts, tows were passed through a chamber containing steam under pressure and having seals at each end through which the tow is passed. These devices suffered from poor sealing and excessive wear of the seals. Also, tow tension was excessive.
Attempts have been made to anneal acrylic tow using steam at atmospheric pressure in a device having no end seals. In these devices, steam penetration of the tow has been poor and frequently the tension necessary to pull the tow through the device has prevented adequate tow shrinkage. Unless the tow is allowed to shrink while in the presence of steam, the filaments will tend to fibrillate under conditions of usage.